Optical fibers are key components in modem telecommunications. Optical fibers are thin stands of glass capable of transmitting an optical signal containing a large amount of information over long distances with very low loss. In essence, an optical fiber is a small diameter waveguide characterized by a core with a first index of refraction surrounded by a cladding having a second (lower) index of refraction. Typical optical fibers are made of high purity silica with minor concentrations of dopants to control the index of refraction.
Broadband light sources for such fiber are useful in a variety of applications. For example contemplated wavelength division multiplexing systems would divide a single broadband light source into a plurality of narrow-band carrier channels, separately modulate the carrier channels and simultaneously transmit the separately modulated channels over a single fiber. Such broadband sources are also potentially useful in fiber sensing systems and in imaging applications.
Unfortunately, conventional light sources fail to provide broad bandwidth light at uniform high levels of power. One conventional approach is to use fibers doped with rare earth elements such as Nd, Er, Yb as spontaneous emission sources. While these sources provide broadband light at low levels of power, their output spectra quickly narrow as the power increases. Moreover, at high pumping powers they tend to lase from small reflections, such as are presented by the fiber endfaces.
Another approach to providing broad bandwidth light is the use of super luminescent diodes. Unfortunately, these devices often fail to provide adequate power, especially after losses incurred in coupling into fiber. Accordingly, there is a need for a new high power, broad bandwidth light source for optical fibers.